Apply PropTypes

In the code editor, take a look at MessageDisplayer's render function.

Notice the expression this.props.message. From this expression, you can deduce that MessageDisplayer expects to get passed a prop named message. Somewhere, at some time, this code is expected to execute:

<MessageDisplayermessage="something"/>

If a component class expects a prop, then you can give that component class a propType!

The first step to making a propType is to search for a property named propTypes on the instructions object. If there isn't one, make one! You will have to declare it after the close of your component declaration, since this it will be a static property.

See the example of a propTypes property on lines 11-13. Notice that the value of propTypes is an object, not a function!

The second step is to add a property to the propTypes object. For each prop that your component class expects to receive, there can be one property on your propTypes object.

MessageDisplayer only expects one prop: message. Therefore, its propTypes object only has one property.